Syntheses and characterization of poly(butylene terephthalate) copolyesters modified with p‐acetoxybenzoic acid

Abstract

Poly(butylene terephthalate) (PBT) copolyesters modified with seven compositions of p-acetoxybenzoic acid (PABA) ranging from 10 to 70 mol % were prepared. The X-ray diffraction patterns, the polarizing microscopy behaviors, and thermal analysis showed that the modified PBT contained more PABA homopolymer units (PABA-PABA) than PBT-PABA units in the copolyesters. On increasing PABA mole percenage, PBT crystallinity decreased and thermal stability increased. It was found that although the PBT copolyesters did not exhibit a clear liquid crystalline texture like the copolyester of poly(ethylene terephthalate) modified with PABA did, the PBT copolyester containing 70 mol % of PABA exhibited the typical shear thinning behavior of a liquid crystalline polymer.

Transcatheter closure of very large (≥ 25 mm) atrial septal defects using the Amplatzer septal occluder

“…The depression of melting temperature was due to the limited crystallite size and the larger amount of crystal imperfection because of the less‐favorable crystallization conditions 9. DSC curves in the heating run revealed double melting peaks for samples 30PBT and 40PBT, which is a widespread observation that has been reported in the literature 10–14. The double melting peaks are marked T m1 and T m2 in Table 1, respectively; and Δ H m is the heat of fusion.…”

Synthesis and Characterization of Novel Thermotropic Aromatic-Aliphatic Biodegradable Copolyesters ContainingD,L-Lactic acid (LA), Poly(butylene terephthalate) (PBT) and Biomesogenic Units

“…The two sharp peaks observed at 1602 and 1500 cm À1 are attributed to the stretch vibrations of C¼C, which belong to the aromatic ring. In addition, it obviously shows that all of the copolyesters exhibit two carbonyl stretching absorption peaks at around 1737 and 1712 cm À1 , which are assigned to aromatic and aliphatic ester bond, respectively [12,24] .…”

“…On the basis of the preceding analysis, the thermal stability of copolyesters are enhanced after introduction of biomesogenic units. [24] , indicating the HBA, VA and LA monomers have been participated in the ester exchange reaction with the BT units during the copolymerization.…”

“…In addition, an additional exothermic peak before the melt transition started is found for all copolyesters, and the intensity of this peak decreases with increasing aromatic biomesogenic units. This may be ascribed to the recrystallization of crystals from butylene terephthalate (BT) segments [24,26] . The same observations could also be found for the polyesters consisting of BT and LA moieties [8] .…”

“…The high content of HBA, VA and LA units involved in the polymerization increases the possibility of PBT segment scission and sequence randomness, thus one could obtain copolyesters with lower melting temperature compared with those prepared from PBT and the second monomer [8,24] . In addition, an additional exothermic peak before the melt transition started is found for all copolyesters, and the intensity of this peak decreases with increasing aromatic biomesogenic units.…”